The grounding is to dissipate static build up when fuel is dropped in the tank. They are not trying to "ground" the tank, just get rid of the static buildup. The reason there is a concern to do this is because (on the Murphy job that I've seen this specification) the tank is fiberglass. The steel risers are backfilled with washed pea gravel or small crushed stone. How good of a ground is this?
I had an electrician working under me once that wired a submerged pump and connected the black to the ground screw and the green to one leg of the pump. When the service techs went to start up the system they called me and said the submerged pump would not work. What was happening was the pump was getting 120 volts instead of 240 volts, and the steel riser that was screwed into the tank (fiberglass) was being energized with 120 volts. No breaker tripped, no explosions, no nothing. I think this indicates the backfill is not a very good ground.
The grounding of the spill containment manhole is someone being very careful trying to prevent problems.